The present invention relates to a process for the extraction of oils from oil-containing seeds, specifically soybeans. More particularly, the invention relates to such a process which provides not only for the extraction and recovery of oils from the seeds but also for the extraction and separate recovery of a lecithin/phosphatide product.
The oilseed industry of the United States produces on an annual basis about thirteen million tons of seedoils from approximately one billion bushels of seed crops, predominantly soybeans. Essentially all of this oil is recovered from the seeds by solvent extraction. Hexane is employed almost exclusively as the solvent in the U.S. today. The oils find primary use in foods, e.g., shortening, margarine, cooking oils, and salad oils, while seed meal from which the oil has been extracted, having a high protein content, is generally processed into animal feeds. About two percent of this meal is further refined for human consumption.
Contact of soybeans with hexane, or with other of the recognized oilseed extraction solvents, extracts not only oils but also significant quantities of other seed components. Of particular importance is a complex mixture of lecithin (phosphatidylcholine) and/or related phosphatide compounds. In part, the lecithin/phosphatide fraction is recovered and used to produce a by-product known in the art as commercial lecithin. In the United States approximately eighty million pounds of commercial lecithin are now produced each year in the course of soybean extraction. Commercial lecithin has recognized utility in a wide variety of services, for instance, as an emulsifier, stabilizer, surfactant, caloric source and/or antioxidant in foodstuffs, cosmetics, soaps, paints, inks, pharmaceuticals, etc. An even greater amount of the soybean lecithin/phosphatide fraction is recovered in the extraction process and then recombined with the extracted seed meal product, an exchange which both upgrades the quality of the oil and enhances the value of the meal as an animal feed.
The recovery of lecithin/phosphatide from oil in the conventional, commercial-scale hexane extraction process involves the extraction of soybeans with the hexane solvent to produce an extract miscella, the evaporation of hexane from the miscella, and the "degumming" of the remaining solution of lecithin/phosphatide in oil. For degumming, the solution is mixed with water at elevated temperature to convert the phosphatide compounds to their hydrate forms. The hydrates, known as gums, are insoluble in the oil and can be removed as a precipitate by settling or centrifugation.
Of particular relevance to the present invention are known processes for the extraction of soybeans with alcohol-based solvents, and specifically alcohol extraction processes in which separation of the extract miscella into solvent and oil is accomplished by phase separation. Solubility of vegetable oil in alcohol solvents is greatly dependent upon temperature. Relatively high solubility of the oils in a lower alcohol solvent at the temperature of the extractor, e.g., 160.degree. to 180.degree. F., permits effective extraction. The extract is subsequently cooled, e.g., to a temperature of about 80.degree. F. or less, substantially lowering the solubility of solvent and oil and permitting their separate recovery by phase separation. The use of an alcohol-based solvent and of phase separation techniques for oil and solvent recovery has substantial advantage from the standpoint of process energy requirements over the use of hydrocarbon solvents and evaporation for the separation of solvent from oil. According to the prior art, a lecithin/phosphatide fraction is extracted from the soybeans by alcohol solvents and subsequently recovered from the miscella in a manner which resembles the degumming procedures which are applied to hexane extracted oils. For instance, Beckel et al report (in U.S. Pat. Nos. 2,445,931, 2,469,147, 2,505,749, and 2,524,037; in an article published in The Journal of the American Oil Chemists' Society, January, 1948, pages 10 and 11, and in an article published in Soybean Digest, May, 1949, pages 20 and 21) that the cooling and/or concentration by evaporation of an ethanol extracted miscella produces a precipitate of nonoil substances which is recovered from either solvent or oil by settling and/or centrifugaton. The nonoil substances are said to include both lecithin and crude sugars. A recent publication by E. C. Baker et al (The Journal of the American Oil Chemists'Society, vol. 60, July, 1983, pages 1271-1277) similarly describes the extraction of soybeans with an isopropanol solvent, the phase separation of resulting miscella into oil and solvent, and a degumming of the oil during subsequent storage by a settling of phosphorus containing compounds.